My experience with my 2017 Volt is that the key fob remote start will use whatever climate control settings were set when the Volt was last turned off. The MyChevrolet App will set whatever it determines is the most effective/efficient settings to cool or heat the cabin to an acceptably comfortable temperature. One reason the MyChevrolet App tends to direct cold air to the front windshield defroster vents may be that the Auto Defogger climate control setting is set On. Try turning off the Auto Defogger and see it that helps.
In the summer, if I park the Volt outside in the sun, before I shut off the Volt I will set the temperature to 60 - 64 F and the fan to maximum (not auto), vents straight ahead, cabin air recirculate, AC to Max. The lower temperature setting seems to help, later on, when I use the MyChevrolet App to precondition the cabin. Related, in the winter when I want maximum cabin heat and don't care about conserving the Volt's EV range I find I get more heat if I don't use Auto for the climate control settings.